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Combined exposure to Maneb and Paraquat alters transcriptional regulation of neurogenesis-related genes in mice models of Parkinson’s disease

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      Abstract

      BackgroundParkinson's disease (PD) is a multifactorial disease where environmental factors act on genetically predisposed individuals. Although only 5% of PD manifestations are associated with specific mutations, majority of PD cases are of idiopathic origin, where environment plays a prominent role. Concurrent exposure to Paraquat (PQ) and Maneb (MB) in rural workers increases the risk for PD and exposure of adult mice to MB/PQ results in dopamine fiber loss and decreased locomotor activity. While PD is characterized by neuronal loss in the substantia nigra, we previously showed that accumulation of α-synuclein in the limbic system contributes to neurodegeneration by interfering with adult neurogenesis.ResultsWe investigated the effect of pesticides on adult hippocampal neurogenesis in two transgenic models: Line 61, expressing the human wild type SNCA gene and Line LRRK2(G2019S), expressing the human LRRK2 gene with the mutation G2019S. Combined exposure to MB/PQ resulted in significant reduction of neuronal precursors and proliferating cells in non-transgenic animals, and this effect was increased in transgenic mice, in particular for Line 61, suggesting that α-synuclein accumulation and environmental toxins have a synergistic effect. We further investigated the transcription of 84 genes with direct function on neurogenesis. Overexpresion of α-synuclein resulted in the downregulation of 12% of target genes, most of which were functionally related to cell differentiation, while LRRK2 mutation had a minor impact on gene expression. MB/PQ also affected transcription in non-transgenic backgrounds, but when transgenic mice were exposed to the pesticides, profound alterations in gene expression affecting 27% of the studied targets were observed in both transgenic lines. Gene enrichment analysis showed that 1:3 of those genes were under the regulation of FoxF2 and FoxO3A, suggesting a primary role of these proteins in the response to genetic and environmental cues.ConclusionsWe report that adult neurogenesis is highly susceptible to multiple “risk factors” for PD, including α-synuclein accumulation, LRRK2 G2019 mutation and exposure to environmental toxins. We identified specific groups of genes that are responsive to each stressor, while uncovering a novel function for Fox transcription factors in PD.

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      Most cited references 34

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      Neurogenesis in the adult human hippocampus.

      The genesis of new cells, including neurons, in the adult human brain has not yet been demonstrated. This study was undertaken to investigate whether neurogenesis occurs in the adult human brain, in regions previously identified as neurogenic in adult rodents and monkeys. Human brain tissue was obtained postmortem from patients who had been treated with the thymidine analog, bromodeoxyuridine (BrdU), that labels DNA during the S phase. Using immunofluorescent labeling for BrdU and for one of the neuronal markers, NeuN, calbindin or neuron specific enolase (NSE), we demonstrate that new neurons, as defined by these markers, are generated from dividing progenitor cells in the dentate gyrus of adult humans. Our results further indicate that the human hippocampus retains its ability to generate neurons throughout life.
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        Parkinson's disease: mechanisms and models.

        Parkinson's disease (PD) results primarily from the death of dopaminergic neurons in the substantia nigra. Current PD medications treat symptoms; none halt or retard dopaminergic neuron degeneration. The main obstacle to developing neuroprotective therapies is a limited understanding of the key molecular events that provoke neurodegeneration. The discovery of PD genes has led to the hypothesis that misfolding of proteins and dysfunction of the ubiquitin-proteasome pathway are pivotal to PD pathogenesis. Previously implicated culprits in PD neurodegeneration, mitochondrial dysfunction and oxidative stress, may also act in part by causing the accumulation of misfolded proteins, in addition to producing other deleterious events in dopaminergic neurons. Neurotoxin-based models (particularly MPTP) have been important in elucidating the molecular cascade of cell death in dopaminergic neurons. PD models based on the manipulation of PD genes should prove valuable in elucidating important aspects of the disease, such as selective vulnerability of substantia nigra dopaminergic neurons to the degenerative process.
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          Systematic discovery of regulatory motifs in human promoters and 3' UTRs by comparison of several mammals.

          Comprehensive identification of all functional elements encoded in the human genome is a fundamental need in biomedical research. Here, we present a comparative analysis of the human, mouse, rat and dog genomes to create a systematic catalogue of common regulatory motifs in promoters and 3' untranslated regions (3' UTRs). The promoter analysis yields 174 candidate motifs, including most previously known transcription-factor binding sites and 105 new motifs. The 3'-UTR analysis yields 106 motifs likely to be involved in post-transcriptional regulation. Nearly one-half are associated with microRNAs (miRNAs), leading to the discovery of many new miRNA genes and their likely target genes. Our results suggest that previous estimates of the number of human miRNA genes were low, and that miRNAs regulate at least 20% of human genes. The overall results provide a systematic view of gene regulation in the human, which will be refined as additional mammalian genomes become available.
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            Author and article information

            Affiliations
            [1 ]Department of Neuroscience, University of California San Diego, 9500 Gilman Dr., MTF 344, La Jolla, CA, 92093-0624, USA
            [2 ]Department of Pathology, University of California San Diego, 9500 Gilman Dr., La Jolla, CA, 92093-0624, USA
            [3 ]Laboratory for Chemistry and Metabolism, Tokyo Metropolitan Institute for Neuroscience, Tokyo, 183-8526, Japan
            Contributors
            Journal
            Mol Neurodegener
            Mol Neurodegener
            Molecular Neurodegeneration
            BioMed Central
            1750-1326
            2012
            28 September 2012
            : 7
            : 49
            23017109
            3502617
            1750-1326-7-49
            10.1186/1750-1326-7-49
            Copyright ©2012 Desplats et al.; licensee BioMed Central Ltd.

            This is an Open Access article distributed under the terms of the Creative Commons Attribution License ( http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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